1. The Field of the Invention
The invention is directed to methods and apparatus for determining when a rotor, caused to rotate by means of a driving arrangement, becomes imbalanced. In particular, the rotor imbalance is determined by sensor means, mechanically connected to the driving arrangement, for sensing a predetermined movement of the driving arrangement and for relaying the sensed movement to evaluation means for determining when the sensed movement indicates rotor imbalance. Response elements generate a warning signal and/or a switch-off signal in response to either rotor imbalance or disruption of the rotor imbalance sensor means.
2. The Relevant Technology
There are many devices which utilize some type of rotating component and, particularly, some type of motor-driven rotor. Imbalance of such a rotor can occur for many reasons and can cause numerous problems including inoperability or defective performance of the device. Rotor imbalance may also cause damage or destruction to the rotor and/or other components of the device. Thus, means for determining when a rotor has become imbalanced, and for switching off a device when rotor imbalance occurs, would be helpful in many devices.
An example of a device having a rotor is a laboratory centrifuge device. It is known from EP 0 455 878 A3 to provide a laboratory centrifuge device with a switch element, forming a unit together with an imbalance element fastened to a drive unit. When imbalanced motions work themselves out into large deflections of the drive unit, a receptacle with a switch fluid located inside opens or closes an electrical transmission pathway by deflection and thus puts out a switch signal for the existing imbalance.
Another example of a device having a rotor is an automatic washing machine. An arrangement for restricting imbalance in fully automatic washing machines is known from DE 31 41 684 A1, in which a bead of mercury, oscillating attenuated in deep resonance, which initiates a contacting process with a pin to thereby effect switching of the drive elements when the maximum permissible imbalance is achieved.
According to the known methods of detecting imbalance, a large deflection of rotors, such as the deflection caused by imbalance in the lower speed range, are detectable by mechanical or electronic sensors. Detection difficulties, however, occur at higher speeds. For example, at high speed, mechanical sensors cannot put out sufficient amplitudes, since the gyroscopic procession produced by the rotor may either increase or decrease the amount of deflection, and thus the triggering of the imbalance will be premature or not occur at all. Moreover, a large mount of adjustment is also necessary for mechanical imbalance sensors.
An example of a particular problem is breakage of the sample containers, often glass tubes, within a laboratory centrifuge device. Such breakage represents a physical hazard to a centrifuge operator and, depending on the nature of the sample material, may also represent a biological hazard. Because the broken sample containers cause rotor imbalance, reliable detection of the rotor imbalance would serve to warn the operator of the possibility of broken sample containers.
It will be appreciated that it would be an advancement in the art to provide methods and apparatus permitting detection of rotor imbalance over the entire speed range of a device having a rotor and, in particular, permitting reliable detection of rotor imbalance at higher speeds.